1. Field of the Invention
The present invention relates generally to the field of internal combustion engine injection systems. More particularly, the invention relates to a technique for controlling gas entrainment in a fuel spray stream of a direct, in-cylinder injection system so as to improve runability and engine performance.
2. Description of the Related Art
Various systems have been developed for providing fuel delivery to internal combustion engines. In gasoline engines, for example, conventional approaches include carbureted fuel delivery, and fuel injection. Among fuel injection systems, a range of solutions are provided by existing technologies, including electronic fuel injection in which fuel delivery is controlled by electronic circuitry. Such systems provide for excellent control of fuel delivery across a range of operating conditions, particularly desired torque and speed ranges. In general, a fuel is injected either directly into a combustion chamber, or at an inlet side of the combustion chamber in a moving air stream. While such techniques are useful in both two-stroke and four-stroke engines, they have become increasingly popular in two-stroke engines due to the greatly improved emissions controls affordable through direct, in-cylinder injection.
In one known type of in-cylinder injection, a liquid fuel is dispersed within a cylinder under the influence of a pressure impulse developed by a linear electric motor and pump. By appropriately controlling the timing and waveform of driving signals applied to the motor, various volumes and rates of fuel delivery can be obtained. Other in-cylinder injection systems employ a mixture of air and fuel. These systems may also employ electrically-driven pumps for delivery of the mixture. Furthermore, injection systems are known in which a pressurized fuel supply, typically delivered in a fuel rail, is coupled to delivery mechanisms such as solenoid-operated valves. The valves may be opened and closed to allow for flow of the pressurized fuel into the combustion chambers.
In each of the various types of in-cylinder fuel injection, sprays of fuel are developed that both distribute the fuel and air, enhance mixing of the fuel and air, and finely atomize the fuel for improved combustion. While the nature of the fuel spray may be altered by such factors as impingement on a piston surface or deflection from various moving and static surfaces, the maintenance of the desired shape and distribution of the fuel spray is often extremely important in maintaining a good fuel distribution and combustion. When operating parameters and mechanical tolerances alter the timing or distribution of the spray within the combustion chamber, significant changes in engine performance may be observed. The degradation of engine performance, which, in certain cases may even pose issues of runability of the engine, may occur both as a result of the basic engine and component design, as well as due to factors which may change during the life of the machine.
There is a need, at present, for an improved technique for internal combustion engine design, particularly in the area of direct, in-cylinder fuel injected engine design. Within this field, there is need for an approach to component design and layout which enhances combustion and runability of an engine by careful control of distribution and maintenance of a fuel spray delivered by direct, in-cylinder injection nozzle.
The present technique offers a design for internal combustion engines which contemplates such needs. The technique is applicable to a variety of fuel injection systems, and is particularly well suited to pressure pulsed designs, in which fuel is pressurized for injection into a combustion chamber by a reciprocating electric motor and pump. However, other injection system types may benefit from the technique described herein, including those in which fuel and air are admitted into a combustion chamber in mixture.
The present technique provides a design for a combustion chamber which limits or controls gas entrainment into a fuel spray. In accordance with aspects of the technique, an injection nozzle is disposed within a recess of a combustion chamber, typically in the cylinder head. The recess houses the fuel injection nozzle, and permits a spray from the nozzle to be injected directly into the combustion chamber. The geometry and disposition of the recess are selected such that gas entrainment into the fuel spray is maintained at desired levels during operation. The recess may include straight, convergent, divergent, or similar sections, and may comprise several such sections along its length. Moreover, the geometry of areas of the combustion chambers adjacent to the recess may aid in controlling gas entrainment. The component structures thus allow the engine designer to permit relative levels of gas entrainment so as to affect the fuel spray in desired manners. For example, very little gas entrainment may be desired to maintain a desired spray profile, such as in a hollow cone. Other levels of gas entrainment may be selected to provide more mixing within the cone, or to provide solid or semi-solid spray cones.